I've got the Voyager...it's a solid phone on a much better network than AT&T.
I have a Blackberry via AT&T for work and the call/data coverage on it absolutely sucks!
There were so many dead spots by my house they had to erect a tower not far away. And forget trying to use it in the Metro/Amtrak! But the Voyager works just fine...and I can change the battery myself!
Web surfing on the iPhone and syncing music with iTunes is superior to the Voyager. Plus, third party developers have come up with pretty cool apps/widgets for the iPhone.
However, everything else in the same if not better on the Voyager. Tactile feedback, emails and texting via QWERTY keypad, voice quality and overall national coverage are superior on the Voyager/verizon network. The broadband speeds on the Verizon network are plenty fine for me and no viruses on the Voyager either!
I've used both a lot so it comes down to what you'll be using it for. Since I text and email a lot, the Voyager is a better choice for me since it has the physical QWERTY keypad. Also, I can't stand AT&T's dead-spot ridden network so I stayed with Verizon's. If you plan on surfing the web primarily and want to sync your MP3's with iTunes, then go with the iPhone.